Have Jenkins ignore .pyc files when using git

Summary:
Developers have this set up via the khan-dotfiles repo so I copied that
approach. deploy.py was failing due to having "local changes" whenever
.pyc files were generated by importing Python code from a submodule that
lacked a gitignore for .pyc files, i.e., third_party/gae-pytz-khansrc

Test Plan:
A submodule within the Jenkins workspace was showing as modified because
of .pyc files within it. AFter I applied the global config settings in
the jenkins user's home directory, these .pyc files were ignore.

Reviewers: csilvers

Reviewed By: csilvers

Differential Revision: http://phabricator.khanacademy.org/D2654